Robotics is an active area of research, and many different types of robotic vehicles have been developed for various tasks. For example, unmanned aerial vehicles have been quite successful in military aerial reconnaissance. Less success has been achieved with unmanned ground vehicles (UGVs), however, in part because the ground or surface environment is significantly more variable and difficult to traverse than the airborne environment.
Unmanned ground vehicles face many challenges when attempting mobility. Surface terrain can vary widely, including for example, loose and shifting materials, obstacles, or vegetation on dry land, which can be interspersed with aquatic environments such as rivers, lakes, swamps or other small bodies of water. A vehicle optimized for operation in one environment may perform poorly in other environments.
There are also tradeoffs associated with the size of vehicle. Large vehicles can handle some obstacles better, including for example steps, drops, gaps, and the like. On the other hand, large vehicles cannot easily negotiate narrow passages or crawl inside small spaces, such as pipes, and are more easily deterred by vegetation. Large vehicles also tend to be more readily spotted, and thus are less desirable for discrete surveillance applications. In contrast, while small vehicles are more discrete, surmounting obstacles becomes a greater mobility challenge.
A variety of mobility configurations have been adapted to travel through variable surface and aquatic environments. These options include legs, wheels, tracks, propellers, oscillating fins and the like. Legged robots can be agile, but use complex control mechanisms to move and achieve stability and cannot traverse deep water obstacles. Wheeled vehicles can provide high mobility on land, but limited propulsive capability in the water. Robots configured for aquatic environments can use propellers or articulating fin-like appendages to move through water, but which may be unsuitable for locomotion on dry land.
Options for amphibious robots configured for both land and water environments are limited. Robots can use water tight, land-based mobility systems and remain limited to shallow bodies of water. They can also be equipped with both land and water mobility devices, such as a set of wheels plus a propeller and rudder, but this adds to the weight, complexity and expense of the robot.
Another option is to equip the amphibious robot with a tracked system. Tracked amphibious vehicles are well-known and have typically been configured in a dual track, tank-like configuration surrounding a buoyant center body. However, the ground-configured dual tracks which are effective in propelling and turning the vehicle on the ground can provide only a limited degree of propulsion through water, and the vehicle's power system must often be over-sized in order to generate an acceptable amount of thrust when traveling in amphibious mode. Furthermore, the differential motion between the two treaded tracks cannot provide the vehicle with the same level of maneuverability and control in water as it does on land, dictating that additional control structures, such as a rudder, also be added to the vehicle for amphibious operations. Another drawback is that typical tracked amphibious vehicles also cannot operate submerged.